1. Field of the Invention
The present invention relates to a method of inspecting a wrap-fitted state (tightened state) of a cap wrap-fitted to the neck of a bottle and to an apparatus therefor. More specifically, the invention relates to a method capable of easily confirming a wrap-fitted state of a cap from one direction without opening the cap and to an apparatus therefor.
2. Description of the Related Art
In a bottle-cap assembly comprising a glass bottle or a plastic bottle and a cap having a tamper-evidence function for clearly indicating that the cap was once opened, it is essential that the cap is fitted in a completely sealed state after the content has been filled. So far, the fitted state was inspected by picking up some samples out of the products, really opening the cap to measure the torque for opening the cap and the angle of fitting.
However, the pick-up inspection is of a nature that is conducted for only some of the products. If the samples are picked up in a large number to improve the reliability of inspection, the cost of production increases correspondingly.
In the wrap-fitting machine used for wrap-fitting the cap to the neck of the bottle, further, the torque is determined at the time of setting, first, the wrap-fitting condition according to the wrap-fitting angle to ensure a basic sealing performance. It is therefore desired that the wrap-fitting angle be easily measured.
To solve this problem, there has been proposed a bottle-cap assembly which enables the fitted state of the cap to be easily confirmed.
For example, Japanese Unexamined Patent Publication No. 12046/1997 discloses a sealing device in which one or a plurality of position indicator marks are formed at predetermined positions lower than the lower end of a plastic cap in a state where the cap is completely screwed onto the neck of a container, and seal indicator marks are formed on a skirt of the cap so as to be located by the side of the position indicator marks in a state where the cap is completely screwed onto the neck of the container.
Japanese Unexamined Patent Publication No. 203512/1998 discloses a method of inspecting the sealed state of the neck of a container by arranging marks on the outer periphery of the container and on the outer surface of a screw cap screwed onto the neck of the container, the marks having a predetermined positional relationship with respect to the ends of the respective threaded portions, and judging whether the screwed state of the screw cap is proper based on the positional relationship of the pair of marks (mark of the container and mark of the screw cap) after the screw cap has been mounted.
Japanese Unexamined Patent Publication No. 11504/1999 discloses a structure for sealing bottles by providing marks that can be viewed from the outer side on a portion corresponding to the starting end of the threaded portion at the neck of the bottle and on a portion corresponding to the terminating end of the threaded portion of the cap, to inspect the degree of the cap wrap-fitted to the neck of the bottle relying upon the positions of these two marks after the bottle is filled with the liquid and is sealed.
Further, Japanese Unexamined Patent Publication No. 118515/2000 discloses an inspection method in which a portion of a cap mounted on the container body is imaged by using a camera, the imaged data is stored, and it is judged whether the mounting state of the cap is acceptable using the imaged data based upon a positional relationship between a reference position of the container body and a reference position of the cap. There has been described that the imaging is effected by using a first camera and a second camera arranged in parallel along the container conveyer passage.
According to the above prior arts, the fitted state of the bottle-cap assembly can be confirmed without relying upon the inspection method of picking up the samples and really opening the caps.
According to the sealing device of Japanese Unexamined Patent Publication No. 12046/1997, however, the marks formed on the bottle and on the cap must be positioned on a straight line or to establish a predetermined relationship, involving difficulty in setting the marks.
According to the method of inspecting the sealed state of Japanese Unexamined Patent Publication No. 203512/1998 and the sealing structure of Japanese Unexamined Patent Publication No. 11504/1999, a predetermined reference range is provided concerning the positional relationship of the cap and the bottle, and the bottle-cap assemblies outside this range are excluded. Therefore, there does not arouse the problem of the sealing device of Japanese Unexamined Patent Publication No. 12046/1997. In the bottle-cap assemblies disclosed in these prior arts, however, the mark of the cap is formed on the side surface of the cap due to the relationship to the bottle. In order to confirm that the marks of the bottle and of the cap are in a predetermined positional relationship, it is necessary to measure the mark from the side surface of the bottle-cap assembly. However, the bottle-cap assemblies filled with the content and sealed with the caps are conveyed on the conveyer along the production line while changing their directions in a random fashion, and the marks formed on the bottle and on the cap are not necessarily headed toward the inspection device. Therefore, failure in the fitted state of the cap is often overlooked decreasing the reliability of inspection.
In order to prevent the bottle-cap assemblies which are in a defectively fitted state from being overlooked, it is necessary to install a plurality of cameras in the circumferential direction, often causing the inspection device to become complex and making it difficult to continuously supply the bottle-cap assemblies.
When the mark (bottle mark) formed on the bottle and the mark (cap mark) formed on the cap are imaged by using a camera and the wrap-fitted state of the cap is inspected based on the obtained image, it is necessary that the two marks are vividly imaged. As for the bottle mark, however, it is often difficult to vividly image the bottle mark. That is, the bottle mark, in many cases, is formed on a portion on the outer surface of the neck of the bottle that is not covered with the cap, i.e., formed on a support ring. In many of the bottles, however, the neck portion equipped with a portion forming a bottle mark such as a support ring is whitened due to crystallization, or the whole bottle inclusive of the neck is formed transparent. When the bottle has the transparent neck, in particular, the bottle mark is not, in many cases, vividly imaged. The bottle wrap-fitted with the cap has been filled with the content liquid such as a beverage. However, since the neck of the bottle is transparent, the swinging level of the liquid in the bottle is reflected on the image caught by the camera and, as a result, the bottle mark is blurred.
It is therefore an object of the present invention to provide a method of inspecting a wrap-fitted state of a cap, which is capable of reliably confirming the wrap-fitted state of the cap that is fitted to the bottle from the upper side in the axial direction of the bottle without opening the cap, easily by using one camera, free of inconvenience involved in the prior art, and a device therefor.
Another object of the present invention is to provide a method of inspecting a wrap-fitted state of a cap by imaging the bottle mark and the cap mark by using a camera, wherein the bottle mark and the cap mark are vividly imaged even for transparent bottles having transparent necks irrespective of the kinds of the bottles, enabling the wrap-fitted state of the cap to be reliably inspected based upon the image processing.
According to the present invention, there is provided a method of inspecting a wrap-fitted state of a cap of a bottle-cap assembly in which the cap having a top panel and a skirt is wrap-fitted to a neck of a bottle, by detecting a positional relationship between a bottle mark formed on the bottle and a cap mark formed on the cap; wherein
an optical lens is arranged at a higher position on the vertical center axis of said bottle-cap assembly in a manner that the vertical center axis is in agreement with an optical axis thereof;
a single camera is arranged at a higher position on the optical axis of said optical lens to image the bottle mark and the cap mark through the optical lens;
an illumination device is arranged for illuminating the bottle mark and the cap mark or the vicinities thereof; and
the bottle mark and the cap mark are simultaneously shot by the camera, and the obtained image is sent to an image processor to detect a positional relationship between the bottle mark and the cap mark.
According to the inspection method of the present invention, the bottle mark and the cap mark are read out from the image data received by the image processor into polar coordinates with the cap as a center and, as required, are expanded to detect the positions thereof, the angle or the distance of expansion between the bottle mark and the cap mark is calculated, and whether the wrap-fitted state is acceptable is judged relying upon the angle or the expanded distance.
According to the inspection method of the present invention, further, it is desired that the illumination device is arranged to surround the optical lens, the optical path of light irradiated from said illumination device is so adjusted that the bottle mark and the cap mark are not directly irradiated with light but the portions of the skirt of the cap without forming the cap mark are directly irradiated with light, and the bottle mark and the cap mark are simultaneously shot by the camera while effecting the illumination by the illumination device under these conditions. Upon imaging the cap mark and the bottle mark under the above-mentioned illumination conditions, the cap mark and the bottle mark are vividly imaged even when the neck portion of the bottle inclusive of the support ring is transparent.
According to the present invention, further, there is provided a device for inspecting a wrap-fitted state of a cap of a bottle-cap assembly in which the cap is wrap-fitted to the neck of a bottle, by detecting a positional relationship between a bottle mark formed on the neck of the bottle and a cap mark formed on the cap, comprising:
an optical lens arranged at a higher position on the vertical center axis of said bottle-cap assembly in a manner that the optical axes thereof are in agreement;
a single camera for simultaneously shooting the bottle mark and the cap mark through said optical lens;
an illumination device for illuminating said bottle mark and said cap mark or the vicinities thereof; and
an image processor for reading out the bottle mark and the cap mark from the image data shot by the camera, expanding, as required, the bottle mark and the cap mark to detect the positions thereof, calculating the angle or the distance of expansion between the bottle mark and the cap mark, and judging whether the wrap-fitted state is acceptable relying upon the angle or the expanded distance.